The art of lithographic printing is based on the immiscibility of ink and water. A lithographic printing plate is composed of ink receptive regions, commonly referred to as the xe2x80x9cimage area,xe2x80x9d generated on a hydrophilic surface of a substrate. When the surface of the printing plate is moistened with water and printing ink is applied, exposed portions of the hydrophilic surface retain the water and repel the printing ink, and the oleophilic image area accepts the printing ink and repels the water. The printing ink retained on the oleophilic image area may then be transferred to the surface of a material upon which the image is to be reproduced. Typically, the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the desired surface.
One method for forming or generating an oleophilic image area on a substrate is by coating the substrate with a radiation-sensitive layer, and then exposing a portion of the layer to IR or UV radiation. The unexposed portion of the coated substrate (negative-working plates) or the exposed portion of the coated substrate (positive-working plates) then undergoes chemical development to form the oleophilic image area. One drawback to using printing plates incorporating this method of producing an oleophilic image area is that, after exposing the radiation-sensitive layer to radiation, the plates must be subjected to chemical processing (e.g., development in an alkaline solution) to form the image area.
An alternative method for forming an oleophilic image area on a substrate is by imagewise applying an ink jettable composition onto the substrate. Ink jetting of an oleophilic image area may be desirable because it requires no chemical processing prior to use. There are a variety of oleophilic materials suitable for ink jetting onto a substrate to form an oleophilic image area. Generally, these materials are soluble in either aqueous or organic carriers. For example, U.S. Pat. Nos. 6,359,056 and 6,131,514, and PCT Published Applications WO /0037254 and WO 01/34934 all report ink jettable materials that are soluble or form dispersions in aqueous solutions. However, for certain applications, it may be desirable to employ an oleophilic material that is soluble in an organic carrier.
In one embodiment, the present invention provides a method of preparing a printing plate. An ink jettable composition composed of an oleophilic polymer in substantially organic solvent is imagewise applied onto a substrate. The oleophilic polymer is then adhered to the substrate. Oleophilic polymers for use in this invention contain polar moieties, with the exception of nitrogen-containing heterocyclic moieties, and the moieties are essentially chemically unchanged when adhered to the substrate. Methods of adhering the oleophilic polymer include air or oven drying the printing plate and/or exposing the printing plate to UV light.
The oleophilic polymer used in the ink jettable composition of the present invention may be film-forming and adhere to the surface of the substrate to form an oleophilic image area. The oleophilic polymer generally contains polar moieties and is compatible with suitable organic solvents. Suitable oleophilic polymers include polyester resins, diazonium compounds, acrylic acid polymer derivatives, acetal resins, polyamide resins and phenolic resins. Suitable organic solvents include benzyl alcohol, 2-phenoxyethanol, diethyl ketone/methyl lactate/water, 1-methoxypropan-2-ol and ethyl-3-ethoxypropanol.
In another embodiment, the present invention provides a method of forming an image on a substrate. An ink jettable composition composed of an oleophilic polymer in substantially organic solvent is imagewise applied onto a substrate. The oleophilic polymer has polar moieties, with the exception of nitrogen-containing heterocyclic moieties.
In yet another embodiment, the present invention provides a lithographic printing plate composed of a substrate and an oleophilic image area. The oleophilic image area is composed of an oleophilic polymer and may contain other nonvolatile components or additives of the ink jettable composition. The oleophilic polymer includes polar moieties with the exception of nitrogen-containing heterocyclic moieties.
The ink jettable composition of the present invention has several characteristics beneficial for forming oleophilic image areas. First, the composition is suitably oleophilic to uptake ink to provide an inked image, but may readily transfer the inked image to a desired medium. Second, the composition forms a thin-film that adheres well to a variety of substrates to form a durable image area. Third, oleophilic image areas formed by the ink jettable composition of the present invention require no additional chemical processing prior to use.
The present invention provides an ink jettable composition capable of forming oleophilic image areas on a substrate for use in a variety of printing plate applications. In one embodiment, an ink jettable composition according to the present invention includes an oleophilic polymer having polar moieties in a substantially organic solvent.
Suitable oleophilic polymers according to the present invention adhere effectively to a substrate and include polar moieties. In certain embodiments, the polymer may be composed of a polymeric backbone with one or more polar moieties. Suitable polar moieties may include carboxyl, hydroxyl, carbonyl, amine, amide, ammonium or sulfate groups. However, the polymer is free of nitrogen-containing heterocyclic moieties.
Examples of suitable polymers having polar moieties include derivatives of polyester resins, diazonium compounds, acrylic acid polymers, acetal resins, phenolic resins, polyamide resins and combinations thereof.
Suitable polyester resin derivatives include, for example, polyester acrylate, polyester resins having a phenolic hydroxyl group, and polyesters formed from p-hydroxybenzoic acid containing hydroxyl and carboxylate moieties. In one embodiment, the polyester resin is formed as a reaction product of diethyl-p-phenylenediacrylate and 1,4-bis(xcex2-hydroxyethoxy)-cyclohexane, referred to hereinafter as Polymer A.
Other suitable resins include polymeric diazonium compounds or a mixture of polymeric diazonium compounds. A variety of these materials are known. These compounds may be prepared, for example, by condensation of monomers, such as monomers described in DE 2024244, with a condensation agent, such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde or benzaldehyde. Furthermore, mixed condensation products may be used which, apart from the diazonium salt units, comprise other non-photosensitive units which are derived from condensable compounds, in particular from aromatic amines, phenols, phenol ethers, aromatic thioethers, aromatic hydrocarbons, aromatic heterocycles or organic acid amides.
Especially useful polymeric diazonium compounds are reaction products of diphenylamine-4-diazonium salts, optionally having a methoxy group in the phenyl group bearing the diazonium salt units, with formaldehyde or 4,4-bis-methoxy-methyl diphenyl ether. Dihydrogen phosphate, hexafluorophosphate, hexafluoroantimonate, hexafluoroarsenate, tetrafluoroborate, and aromatic sulfonates such as 4-tolyl-sulfonate or mesitylene sulfonate are particularly suitable counterions for these polymeric diazo resins.
In one embodiment, the diazonium compound is derived from the condensation of 3-methoxy-diphenylamine-4-diazonium sulfate and 4,4xe2x80x2-bis-methoxymethyldiphenylether isolated as the mesitylene sulfonate salt and is available under the tradename NEGA 107 from Panchim, Lisses, France.
Suitable acrylic acid polymer derivatives may include acrylic resins containing one or more monomers having an acidic group, for example polyhydroxystyrene, polyhalogenated hydroxystyrene, N-(4-hydroxyphenyl)methacrylamide, hydroquinone monomethacrylate, N-(sulfamoylphenyl)methacrylamide, N-phenylsulfonylmethacrylamide, N-phenylsulfonylmaleimide, acrylic acid, and methacrylic acid.
Examples of suitable phenolic resin derivatives include Novolak resins, resole resins, Novolak/resole resins and polyvinyl phenol resins. Novolak resins are polymers that are derived by the polycondensation of at least one kind of aromatic compound such as phenol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, resorcin, pyrogallol, bisphenol A, trisphenol, o-ethylphenol, m-ethylphenol, p-ethylphenol, propyl phenol, n-butylphenol, t-butylphenol, 1 -napthol and 2-napthol, with at least one aldehyde such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, fufuralor, or ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone and other aldehyde-releasing compounds capable of undergoing phenol-aldehyde condensation in the presence of an acid catalyst. Typical Novolak resins include, but are not limited to, phenol-formaldehyde resin, cresol-formaldehyde resin, phenol-cresol-formaldehyde resin, p-t-butylphenol-formaldehyde resin, and pyrogallol-acetone resins.
Resole resins are formed as the condensation product of bis-phenol A and formaldehyde. Examples of suitable resole resins include R17620, a phenol/formaldehyde resole resin sold by B.P. Chemicals Ltd. of Sully, Wales, SMD995, an alkyl phenol/formaldehyde resole resin sold by Schnectady Midland Ltd. of Wolverhampton, England, UCAR phenolic resin BKS-5928 from Georgia Pacific Corporation and Uravar FN6, an alkyl phenolic resole resin sold by DSM Resins UK, South Wirral, UK.
Suitable polyvinyl compounds may be synthesized by radical polymerization or cationic polymerization of one or more hydroxystyrene derivatives. The polyvinyl phenol may be at least partially hydrogenated. It may also be composed of a resin in which OH groups of the phenols are protected with a t-butoxycarbonyl group, a pyranyl group, or a furanyl group. Suitable polyvinyl phenols include polyhydroxystyrenes and copolymers containing recurring units of a hydroxystyrene, and polymers and copolymers containing recurring units of halogenated hydroxystyrenes. Specific examples of suitable polyvinyl phenol compounds include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, 2-(o-hydroxyphenyl)propylene, 2-(m-hydroxyphenyl)propylene and 2-(p-hydroxyphenyl)propylene.
Examples of suitable acetal resins may include polyvinyl acetal resin, formal resin and butyral resin. One example of an acetal resin is a binary acetal polymer that is composed of recurring units which include two six-member cyclic acetal groups, one of which is unsubstituted or substituted with an alkyl or hydroxyalkyl group and the other of which is substituted with an aromatic or heterocyclic moiety as disclosed in U.S. Pat. No. 5,169,897. Another example is an acid-substituted ternary acetal polymer composed of recurring units which include three six-member cyclic acetal groups, one of which is unsubstituted or substituted with an alkyl or hydroxyalkyl group, another of which is substituted with an aromatic or heterocyclic moiety, and a third of which is substituted with an acid group, an acid-substituted alkyl group or an acid-substituted aryl group as disclosed in U.S. Pat. No. 5,219,699. Yet another example of an acetal polymer is reported in U.S. Pat. No. 5,534,381. A further example is a polyvinyl acetal resin which contains 4 to 40 mol-% vinyl alcohol units, 1 to 20 mol-% vinyl acetate units, 0 to 85 mol-% vinyl acetal units derived from an aldehyde free of hydroxyl groups and 1 to 85 mol-% vinyl acetal units derived from an aldehyde containing hydroxyl groups as described in U.S. Pat. No. 4,940,646. In one embodiment, the acetal resin is derived from polyvinyl alcohol in which 19.5 mol percent of the hydroxyl groups are functionalized with acetaldehyde, 45.6 mol percent of the hydroxyl groups are functionalized with butyraldehyde, 10.3 mol percent of the hydroxyl groups are functionalized with 4-carboxybenzaldehyde, 1.5 mol percent of the hydroxyl groups are functionalized with ethanoic acid and 23.1 mol percent of the hydroxyl groups are unfunctionalized, referred to hereinafter as Polymer B.
Examples of suitable polyamide resins include sulfonamide monomers and methacrylamide monomers. Other suitable copolymers may include between 10 to 90 mol % of a sulfonamide monomer unit, such as N-(p-aminosulfonylphenyl)methacrylamide, N-(m-aminosulfonylphenyl)methacrylamide, N-(o-aminosulfonylphenyl)methacrylamide, and/or the corresponding acrylamide. Useful alkaline developer soluble polymeric materials that comprise a pendent sulfonamide group and their method of preparation are disclosed in U.S. Pat. No. 5,141,838, incorporated herein by reference.
The oleophilic polymers described above may be soluble in substantially organic solvents, while being insoluble in predominantly aqueous solutions. Suitable organic solvents will depend on the specific oleophilic polymer being used, and generally include alcohols, ketones, and aliphatic and aromatic hydrocarbons. For example, the solvent may include benzyl alcohol, 2-phenoxyethanol, diethyl ketone/methyl lactate/water or 1-methoxypropan-2-ol. Other suitable solvents may include dimethyl formamide, tetrahydrofuran, methyl cellosolve, n-hexane, cyclohexane, trichloroethane, carbon tetrachloride, toluene, ethyl acetate, trichloroethylene, methyl ethyl ketone, methyl acetate, cyclohexanone, dioxane, acetone, carbon disulfide, nitrobenzene, nitromethane, ethanol, dimethyl sulfoxide, ethylene carbonate, phenol, methanol and ethyl-3-ethoxy propanol. As described in further detail below, these solvents may be at least partially dried or evaporated after imagewise applying the composition onto the substrate.
Optionally, the composition of the present invention may include or further comprise nonvolatile components or additives commonly used in inkjet fluid compositions. For example, the composition may include a variety of surfactants, humectants, biocides, viscosity builders, colorants, dyes, pH adjusters, drying agents, defoamers and combinations thereof. Examples of suitable surfactants include ZONYL surfactant supplied by Dupont, SURFYNOL surfactant supplied by Air Products and AEROSOL surfactant supplied by Cyanamid. An example of a suitable humectant is ethandiol. Suitable biocides include PROXEL GXL supplied by Zeneca Colors and KATHON XL supplied by Rohm and Haas. An example of a suitable viscosity builder is polyethylene glycol. The composition may also include dyes such as Ethyl Violet, Crystal Violet, Malachite Green, Brilliant Green, Victoria Blue B, Victoria Blue R and Victoria Pure Blue BO.
The ink jettable composition of the present invention may be applied to a substrate to form an oleophilic image area suitable for use in printing plate applications. Suitable substrates have hydrophilic surfaces, and generally include metals, polymeric films, ceramics, stiff papers, or a laminate of these materials. Suitable metal substrates include aluminum, zinc, titanium and alloys thereof. Suitable polymeric supports, such as polyethylene terephthalate film, may be coated with hydrophilicity-enhancing components, including alkoxysilanes, aminopropyltriethoxysilane, glycidoxypropyltriethoxysilane and epoxy functional polymers. The substrate may be of sufficient thickness to sustain the wear from printing and be thin enough to wrap around a printing form. Typical substrate thickness ranges from about 100 to about 600 xcexcm. Adhesion of the oleophilic polymer may be increased by treating the surface of the substrate prior to application of the oleophilic polymer. For example, the surface of an aluminum substrate may be treated by anodizing and/or graining to promote adhesion of the oleophilic polymer. Specific examples of suitable substrates and substrate treatments are provided in Table 1 below.
In Table 1 above, the abbreviation xe2x80x9cAAxe2x80x9d refers to xe2x80x9cas anodized.xe2x80x9d An aluminum surface is quartz grained and then anodized using DC current of about 8 A/cm2 for 30 seconds in a H2SO4 solution (280 g/liter) at 30xc2x0 C.
xe2x80x9cEGxe2x80x9d means xe2x80x9celectrolytic graining.xe2x80x9d The aluminum surface is first degreased, etched and subjected to a desmut step (removal of reaction products of aluminum and the etchant). The plate is then electrolytically grained using an AC current of 30-60 A/cm2 in a HCl solution (10 g/liter) for 30 seconds at 25xc2x0 C., followed by a post-etching alkaline wash and a desmut step. The grained plate is then anodized using DC current of about 8 A/cm2 for 30 seconds in a H2SO4 solution (280 g/liter) at 30xc2x0 C.
xe2x80x9cPVPAxe2x80x9d is a polyvinylphosphonic acid. A plate is immersed in a PVPA solution and then washed with deionized water and dried at room temperature.
xe2x80x9cPFxe2x80x9d means that the substrate has a phosphate fluoride interlayer. The process solution contains sodium dihydrogen phosphate and sodium fluoride. An anodized substrate is treated in the solution at 70xc2x0 C. for a dwell time of 60 seconds, followed by a water rinse and drying. The sodium dihydrogen phosphate and sodium fluoride are deposited as a layer to provide a surface coverage of about 500 mg/M2.
xe2x80x9cG20xe2x80x9d is a printing plate substrate described in U.S. Pat. No. 5,368,974, which is incorporated herein by reference.
xe2x80x9cSilxe2x80x9d means that an anodized plate is immersed in a sodium silicate solution to coat it with an interlayer. The coated plate is then rinsed with deionized water and dried at room temperature.
xe2x80x9cDSxe2x80x9d means xe2x80x9cdouble sided smooth.xe2x80x9d As aluminum oxide plate is degreased, etched or chemically grained, and subjected to a desmut step. The smooth plate is then anodized.
xe2x80x9cPGxe2x80x9d means xe2x80x9cpumice grained.xe2x80x9d The surface of an aluminum substrate is degreased, etched and subjected to a desmut step. The plate is then mechanically grained by subjecting it to a 30% pumice slurry at 30xc2x0 C., followed by a post-etching step and desmut step. The grained plate is then anodized using DC current of about 8 A/cm2 for 30 seconds in a H2SO4 solution (280 g/liter) at 30xc2x0 C. The anodized plate is then coated with an interlayer of, for example, sodium silicate.
xe2x80x9cCHBxe2x80x9d means chemical graining in a basic solution. After an aluminum substrate is subjected to a matte finishing process, a solution of 50 to 100 g/liter NaOH is used during graining at 50xc2x0 C. to 70 xc2x0 C. for 1 minute. The grained plate is then anodized using DC current of about 8 A/cm2 for 30 seconds in a H2SO4 solution (280 g/liter) at 30xc2x0 C. The anodized plate is then coated with a silicated interlayer.
Optionally, prior to application of the ink jettable composition, a surfactant may be applied to the substrate to form a printing plate precursor. The surfactant may improve printing plate image resolution without adversely affecting the adhesion of the ink jettable composition. Suitable surfactants for the present invention include alkylated surfactants, fluorosurfactants and siliconated surfactants.
Suitable alkylated surfactants include sodium dodecylsulfate, isopropylamine salts of an alkylarylsulfonate, sodium dioctyl succinate, sodium methyl cocoyl taurate, dodecylbenzene sulfonate, alkyl ether phosphoric acid, N-dodecylamine, dicocoamine, 1 -aminoethyl-2-alkylimidazoline, 1-hydroxyethyl-2-alkylimidazoline, cocoalkyl trimethyl quaternary ammonium chloride, polyethylene tricecyl ether phosphate and the like.
Examples of suitable fluorosurfactants include ZONYL FSD, ZONYL FSA, ZONYL FSP, ZONYL FSJ, ZONYL FS-62, ZONYL FSK, ZONYL FSO and ZONYL FS-300, all of which are commercially available from E.I. Du Pont De Nemours and Co. Additional examples of suitable fluorosurfactants include FLUORAD FC-135, FLUORAD FC-129, FLUORAD FC-120, FLUORAD FC-100, FLUORAD FC-170C and FLUORAD FC-171, all of which are commercially available from 3M, St. Paul, Minn.
Examples of suitable siliconated surfactants include polyether modified poly-dimethyl-siloxane, silicone glycol, polyether modified dimethyl-polysiloxane copolymer, and polyether-polyester modified hydroxy functional polydimethyl-siloxane.
The precursor plate surfactant may be adsorbed onto the substrate by any conventional method, for example, by immersion of the substrate in an aqueous solution of the surfactant for a suitable period of time. The remaining non-adsorbed surfactant may then be removed from the substrate surface by, for example, rinsing with water, and then drying. The resulting printing plate precursor has an effective amount of surfactant on at least one surface of the substrate to improve printing resolution.
The composition of the present invention may be applied or ink jetted onto the substrate or the printing plate precursor by conventional ink jetting methods to form an oleophilic image region suitable for use in a printing plate. Examples of suitable ink jet printers for use with the compositions of the present invention include the Xaarjet Evaluation Kit, Model No. XJ126R supplied by Xaarjet, Cambridge, UK, the Hewlett Packard DeskJet 970 CXI ink jet printer, the Hewlett Packard 540C ink jet printer, the Epson Stylus Color 600 ink jet printer, the Epson 740 ink jet printer, the Epson 800 ink jet printer, the Epson Stylus Color 900 ink jet printer and the Epson Stylus Color 3000 ink jet printer.
After imagewise applying the composition to the substrate by ink jetting, the oleophilic polymer may be adhered to the substrate. The attractive forces of the polar moieties contained in the polymer may facilitate or enhance the adhesion of the oleophilic polymer to the substrate. The oleophilic polymer may be adhered, for example, by drying the plate or exposing the plate to UV radiation. Suitable drying techniques include air drying and/or oven drying.
In one embodiment, the oleophilic polymer may be adhered to the substrate by drying the plate in a suitable oven at between about 50 and 200xc2x0 C. for between about 30 seconds and five minutes. In another embodiment, the plate may be dried at about 100xc2x0 C. for about one minute.
Alternatively, the oleophilic polymer may be adhered to the substrate by exposing the plate to UV radiation to cure the polymer. In one embodiment, the plate may be exposed to UV radiation provided by one or more 1000 to 5000 Watt multi-spectrum diazonium/photopolymer lamps for at least 10 seconds, more particularly, between 10 seconds and 120 seconds to cure the polymer.
In yet another embodiment, the plate may be oven dried and then exposed to UV radiation. For example, the plate may be oven dried at about 100xc2x0 C. for about 1 minute and then exposed to UV energy for about 25 seconds to cure the composition. The oven drying and curing steps, although optional, may provide improved press durability in certain embodiments.
The adhered oleophilic image area may retain between about 0 w/w percent and 90 w/w percent of the organic solvent after air drying, oven drying and/or UV exposure steps depending on the particular polymer and solvent used. For example, air dried polymeric solutions containing 2-phenoxyethanol exhibited a residual solvent level of about 90 w/w percent, while oven dried polymeric solutions containing the same solvent exhibited a residual solvent level of about 5 w/w percent. In another example, air dried solutions containing acetone exhibited a residual solvent level of about 15 w/w percent, while oven dried solutions containing the same solvent exhibited a residual solvent level of about 14 w/w percent.
The oleophilic image area of the present invention may be a film having a thickness between about 1 and 5 mil, more particularly between about 1 and 2 mil. The oleophilic image area is sufficiently ink-receptive to uptake ink, but may readily transfer the ink to an intermediate blanket or other desired destination. Furthermore, as described in the examples below, embodiments of the present invention demonstrate suitable durability for extended run length without additional processing.